Theme 3 - ECG

Question 1

what type of junctions allow electrical coupling of cells?

Answer 1

gap junctions

Question 2

what is the most numerous cell type in the heart?

Answer 2

contractile cells

Question 3

what is the function of the fibrous skeleton?

Answer 3

electrically isolates the A from V so they don’t contract at the same time

Question 4

how are cardiomyocytes linked?

Answer 4

by gap junctions at intercalated disks

Question 5

what speed to A and V myocytes propagate at?

Answer 5

0.3-0.5m/s

Question 6

what speed do modified myocytes in the purkinje fibres propogate at?

Answer 6

5m/s

Question 7

what three things are intercalated disks made up of?

Answer 7

fascia adherens, gap junctions and desmosomes

Question 8

what allows synchronous conduction of impulses from SA to AV node?

Answer 8

internodal bundles

Question 9

how many specialised bundles are there in the atria and what do they contain?

Answer 9

four bundles that contain purkinje like cells

Question 10

where is Bachman’s bundle found?

Answer 10

inner wall of the LA

Question 11

what is the speed of transmission at the AV node and why?

Answer 11

slow to allow atria to empty blood into the ventricles so that they are full at systole

Question 12

what sequence does depolarisation pass in the ventricular wall?

Answer 12

septum then apex then AV groove

Question 13

what does an ECG show?

Answer 13

individual currents of cardiomyocytes that work together in a functional syncytium

Question 14

what is an ECG lead and where is it connected?

Answer 14

a configuration of electrodes - positive (ankle or leg), negative (wrist) and sometimes a ground electrode

Question 15

how many electrodes does a 12 lead ECG use?

Answer 15

10

Question 16

what type of leads make up 12 standard lead ECG?

Answer 16

3 bipolar leads (frontal plane), 3 augmented leads (coronal plane) and 6 pre cordial leads (thorax near the heart)

Question 17

what does the P wave represent?

Answer 17

depolarisation in atria from SA node

Question 18

what does the PR segment represent?

Answer 18

SA to AV delat to allow ventricular filling

Question 19

what does QRS represent?

Answer 19

movement of electrical activity through the ventricles (both ventricles need to be simultaneously depolarisation)

Question 20

what does ST represent?

Answer 20

beginning of ventricular repol (should be flat)

Question 21

what is the T wave?

Answer 21

ventricular repolarisaton

Question 22

what are escape beats and what do they appear as on ECG?

Answer 22

when ventricles dont get a signal so signals itself and the myocardium beats ineffectively (misshaped QRS)

Question 23

what is a possible cause of wide QRS?

Answer 23

problems in the purkinje system

Question 24

what is a large/deep Q wave a sign of?

Answer 24

dead tissue - old MI

Question 25

what is sinus tachycardia?

Answer 25

fast heart rate due to SA node beating too quickly

Question 26

how is atrial rate calculated?

Answer 26

P to P wave

Question 27

how is ventricular rate calculated?

Answer 27

RR interval (QRS to QRS)

Question 28

how can rate be calculated using boxes on ECG?

Answer 28

this is ventricular rate so counting how many big boxes occur between two R waves then 300/big boxes

Question 29

what are the names of pre cordial leads and what plane do they record from?

Answer 29

transverse - V1-V6

Question 30

what is the main NT in psym control of the heart and what receptors does it work on?

Answer 30

vagal drive from Ash which stimulates muscarinic receptors

Question 31

what drug is a muscarinic antagonist and therefore increases heart rate?

Answer 31

atropine

Question 32

is heart vasculature innervated by the psym system?

Answer 32

no

Question 33

what type of nerves does symp autonomic control work on?

Answer 33

stellate nerves

Question 34

what is the effect of a beta agonist on heart rate and what receptors does it work on?

Answer 34

increases rate via b2 adrenergic receptors

Question 35

what is the effect of beta blockers on heart rate and what receptors does it block?

Answer 35

decreases rate via adrenergic receptors

Question 36

what is AV block?

Answer 36

a delay due to failure of atrial signal to stimulate ventricles

Question 37

what three main things is AV block caused by

Answer 37

- ischaemia of AV node or AV bundles - POOR PERFUSION - compression of AV bundle by scar/calcified tissue - inflammation of AV node or bundle

Question 38

what are the symptoms of AV block?

Answer 38

palpitations, hypotension like - dizziness, malaise, syncope and risk of sudden death - patient can be asymptomatic

Question 39

How is 1st degree heart block characterised on ECG?

Answer 39

increased PR interval (more than 5 small boxes) but all Ps are followed by QRS

Question 40

what is first degree heart block usually due to?

Answer 40

delayed AV node transmission

Question 41

how is Mobitz type I 2nd degree heart block characterised on ECG?

Answer 41

- some P waves are blocked and not followed by QRS | - some missing QRS (P wave gets longer until QRS fails to follow it - wenckebach)

Question 42

what is the cause of mobitz type I 2nd degree heart block and what treatment is usually given?

Answer 42

AV node damage and usually no treatment

Question 43

what are the two types of second degree heart block?

Answer 43

mobitz type I and II

Question 44

how is Mobitz type II 2nd degree heart block characterised on ECG?

Answer 44

consistent PR interval and some P waves blocked/not followed by QRS

Question 45

what causes Mobitz type II second degree heart block?

Answer 45

problems with ventricles or bundle of his

Question 46

is mobitz type II 2nd degree heart block high risk and what is the treatment?

Answer 46

yes it is high risk and treated by implanting a pacemaker

Question 47

how is 3rd degree heart block characterised on ECG?

Answer 47

distance of P to QRS is unrelated and PR interval varies radically

Question 48

what causes 3rd degree heart block?

Answer 48

AV node isn't conducting so ventricles do their own thing (ectopic complex)

Question 49

what are they features of ventricular rate and atrial beats in 3rd degree heart block?

Answer 49

ventricular rate and atrial beats are consistent

Question 50

what is a premature beat?

Answer 50

early neats that can be triggered by irritable tissue

Question 51

what are escape beats and what triggers them?

Answer 51

late beats when the atrial signal is delayed or prevented that are triggered by natural rhythmicity of non atrial tissue

Question 52

what is the purpose of escape beats?

Answer 52

an extra beat to escape arrhythmia

Question 53

How is a premature ventricular contraction characterised on ECG?

Answer 53

Very wide QRS and no T wave, no S wave | - negative dip where T wave should be

Question 54

where are premature ventricular contractions often triggered and what does this result in?

Answer 54

in the middle of the myocardium (non purkinje) | - results in electrical unsynchrony, delayed and insufficient conduction

Question 55

what is atrial fibrillation and what happens?

Answer 55

disorganised electrical activity in the atria | - ventricular rate is faster and irregular as many signals reach the AV node but only some are transmitted

Question 56

how is atrial fibrillation characterised on ECG?

Answer 56

No P wave - flat or wiggly line instead

Question 57

what can AF lead to?

Answer 57

thrombus formation in the atrium due to slow flow of blood | - increased risk of stroke

Question 58

what is respiratory sinus arrhythmia?

Answer 58

heart beat is slight fasting during inspiration and slightly slower during expiration

Question 59

what is respiratory sinus arrhythmia a sign of and who is it most commonly seen in?

Answer 59

a healthy heart mostly seen in children and athletes